The invention relates to the forming of tubular workpieces by internal pressure created by a fluid, i e hydroforming, and in particular to a segmented tool used for said forming operation.
The hydroforming process is described in “Hydroforming—Umformen mit Wirkmedien im Automobilbau, Verlag Moderne Industrie, Landsberg, 2002”. In this process tubes formed to final shape by insertion in a tool where the tubes are expanded by applying an internal pressure to the inside of the tube using a fluid. The tubes may be straight or pre-bent depending on the final requirements.
Hydroforming of large work-pieces, such as sidemembers for car body structures presents significant problems due to the difficulty of handling the very heavy tools that are required as moulds during forming. For this reason segmented tool inserts, i e tools that consists of two or more parts, are sometimes used, which considerably facilitates the handling and makes it possible to exchange parts of the inserts if the insert has been damaged or worn, without replacing the whole tool. To keep the segments in place the tool insert is surrounded by a base block, with tight tolerances to the segmented inserts. The base block may be manufactured in one part or may comprise a base and vertical supports fixed to it. The disadvantage of this arrangement is the high cost for the base blocks and the fact that these base blocks are even heavier and more difficult to handle than single piece inserts. The problems connected with the use of large toolings become particularly pronounced when small series or prototypes are manufactured, which means that the tool has to be replaced frequently. The problem is discussed in “Innenhochdruck-Umformen fur Karosseriekomponenten, 3. Chemnitzer Karosseriekolloquium, CBC 2002, Verlag Wissenschaftliche Scripten, Zwickau”, page 62, where it is suggested that tools for prototypes are manufactured by forming a cavity directly in a single piece of metal and simplified in the sense that no inserts are used. This does not make handling of the tool easier and no possibility to exchange a part of the tool is possible.
In “Hydroforming-Umformen mit Wirkmedien im Automobilbau” segmented inserts are mentioned, but always in combination with base blocks that keep the segments from separating during forming.